U.S. patent number 5,078,891 [Application Number 07/490,207] was granted by the patent office on 1992-01-07 for method of controlling silica deposition in aqueous systems.
This patent grant is currently assigned to Betz Laboratories, Inc.. Invention is credited to Cato R. McDaniel, Truc K. Nguyen, Steven P. Sherwood.
United States Patent |
5,078,891 |
Sherwood , et al. |
January 7, 1992 |
Method of controlling silica deposition in aqueous systems
Abstract
A method for the inhibition of silica deposition on the internal
surfaces of an aqueous system comprising adding to the aqueous
system a phosphonate compound and a water soluble polymer having
the structure: ##STR1## wherein M is a water soluble cation. The
aqueous systems in which the water soluble phosphonate and polymer
are particularly effective on cooling water and boiler systems.
Inventors: |
Sherwood; Steven P. (The
Woodlands, TX), Nguyen; Truc K. (Houston, TX), McDaniel;
Cato R. (The Woodlands, TX) |
Assignee: |
Betz Laboratories, Inc.
(Trevose, PA)
|
Family
ID: |
23947051 |
Appl.
No.: |
07/490,207 |
Filed: |
March 8, 1990 |
Current U.S.
Class: |
210/699; 210/700;
252/180; 252/181; 422/15 |
Current CPC
Class: |
C02F
5/14 (20130101) |
Current International
Class: |
C02F
5/14 (20060101); C02F 5/10 (20060101); C02F
001/00 (); C02F 005/10 () |
Field of
Search: |
;252/180,181,384.2,389.24,395 ;210/697,698,699,700,701
;422/15,17,18,19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Willis, Jr.; Prince
Assistant Examiner: Silbermann; J.
Attorney, Agent or Firm: Ricci; Alexander D. Hill; Gregory
M.
Claims
We claim:
1. A method for inhibiting the deposition of silica containing
material on the inner surfaces of the containment means of an
aqueous medium consisting essentially of adding to said aqueous
medium from about 2.5 to 5.0 parts per million parts of said
aqueous medium of a water soluble phosphonate selected from the
group consisting of:
hydroxyethylidenediphoshonic acid,
2-phosphonobutane-1,2,4-tricarboxylic acid,
hydroxyisobutylidene diphosphonic acid, and
aminotri (methylenephosphonic) acid,
and from about 50 to 100 parts per million parts of said aqueous
medium of a water soluble polymer having repeat units (a) and (b)
comprising the structure: ##STR4## wherein M is a water soluble
cation, the molar ratio of said repeat units a:b is about 3:1 and
the number average molecular weight of said polymer is between
1,000 and 1,000,000.
2. The method according to claim 1 wherein the number average
molecular weight of said polymer is between 1,500 and 500,000.
3. The method according to claim 1 wherein the number average
molecular weight of said polymer is between 1,500 and 10,000.
4. The method according to claim 1 wherein said phosphonate is
hydroxyethylidene diphosphonic acid.
5. The method according to claim 1 wherein said phosphonate is
2-phosphonobutane-1,2,4-tricarboxylic acid.
6. The method according to claim 1 wherein said aqueous medium is a
cooling water system.
7. The method according to claim 1 wherein said aqueous medium is a
boiler water system.
Description
FIELD OF THE INVENTION
The present invention relates to cooling and boiler water systems.
The control of silica deposition within these systems is the focus
of the invention disclosed hereinafter.
BACKGROUND OF THE INVENTION
The problems of scale formation and its attendant effects have
troubled water systems for years. For instance, scale tends to
accumulate on internal walls of various water systems, such as
boiler and cooling systems, thereby materially lessening the
operational efficiency of the system.
One particular type of deposit, silica, has proven to be especially
troublesome. This invention is directed toward those water systems
where silica deposition is most problematic.
In cooling water systems, silica forms a deposit on the metal
surfaces which contact the water flowing through the system. In
this manner, heat transfer efficiency becomes severely impeded.
This, in turn has a deliterious effect on the overall operating
efficiency of the cooling water system.
Although steam generating systems are somewhat different from
cooling water systems, they share a common problem in regard to
deposit formation. As detailed in the Betz Handbook of Industrial
Water Conditioning, 8th Edition, 1980, Betz Laboratories, Inc.,
Trevose, Pa. Pages 85-96, the formation of scale and sludge
deposits on boiler heating surfaces is a serious problem
encountered in steam generation. Although current industrial steam
producing systems make use of sophisticated external treatments of
the boiler feedwater, e.g., coagulation, filtration, softening of
water prior to its feed into the boiler system, these operations
are only moderately effective. In all cases, external treatment
does not in itself provide adequate treatment since muds, sludge,
silts and hardness-imparting ions, such as silica, escape the
treatment, and eventually are introduced into the steam generating
system. As is obvious, the deposition of silica on the structural
parts of a steam generating system causes poorer circulation and
lower heat transfer capacity, resulting accordingly in an overall
loss in efficiency.
Various methods have been utilized for resolving the problem of
sludge and silt, including silica, deposition. In U.S. Pat. No.
3,578,589, Hwa et al., inhibition of scale, mud, silt and sludge
deposition is achieved by adding a nonionic surface active agent,
such as a polyethyleneoxy alkyl phenol, and a water soluble
polymer, such as polyacrylic acid.
In Watsen et al., U.S. Pat. No. 3,948,792, the patentees disclose
the problem of silicate scale formation in automobile and diesel
coolant systems. They teach adding a water soluble carboxylic acid
polymer along with boric acid, or borates, and nitrites.
U. S. Pat. No. 4,869,845, Chen, utilizes the same copolymer as
utilized in the present invention to treat scale and corrosion
problems in cooling and boiler water systems. The copolymer is
added to the system with both a phosphonate and a zinc compound.
The purpose of the copolymer is to maintain the solubility of zinc.
Without this mechanism, the zinc would precipitate in the form of
zinc hydroxide and would be unavailable for its desired
anti-corrosion activity.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the invention, it has been discovered that the
water soluble copolymers, as shown in Formula I hereinafter, are
effective in controlling the formation of silica deposits in
various water systems. ##STR2## wherein M is a water soluble
cation. This polymer is referred to as acrylic acid/allyl hydroxy
propyl sulfonate ether (AA/AHPSE). The IUPAC nomenclature for AHPSE
is 1-propane sulfonic acid, 2-hydroxy-3-(2 propenyl-oxy) mono
sodium salt.
The number average molecular weight of the water soluble copolymers
of FORMULA I may fall within the range of 1,000 to 1,000,000.
Preferably the number average molecular weight will be within the
range of from about 1,500 to about 10,000 being even more highly
desirable. The key criterion is that the polymer be water
soluble.
The molar ratio a:b of the monomers of FORMULA I may fall within
the range of between about 30:1 to 1:20, with the a:b molar ratio
range of from about 10:1 to 1:5 being preferred.
With respect to both repeat units of the polymers of the present
invention, they may exist in acid or water soluble salt form when
used in the desired water system.
As to preparation of the monomer designated as a above, in FORMULA
I, acrylic acid is well known. It may be produced by hydrolysis of
acrylonitrile or via oxidation of acrolein. Other well known vinyl
containing monomers such as methacrylic acid and acrylamide may
also be utilized as monomer a of FORMULA I in accordance with the
invention.
Turning to the allyl containing monomer, monomer b, in FORMULA I
above, it may be produced by reacting allyl alcohol with a
non-tertiary alcohol in the temperature range of about
25.degree.-150.degree.C. as detailed in U.S. Pat. No. 2,847,477
(the entire disclosure of which is hereby incorporated by
reference) followed by, if desired, sulfonation, phosphorylation,
phosphonation or carboxylation of the monomer via well-known
techniques.
The preferred allyl hydroxyl propyl sulfonate ether monomers
(monomer b, FORMULA II) may conveniently be prepared via a ring
opening reaction of the epoxy group of an allyl glycidyl ether
precursor. Sulfonation of the epoxy group with sodium sulfite in
the presence of a phase transfer catalyst such as tetra-n-butyl
ammonium bisulfite or with fuming sulfuric acid containing sulfur
trioxide will produce the sulfonic acid group and hydroxy group of
the AHPSE. The resulting monomer can be further neutralized with
caustic or other basic material. The reaction is illustrated by the
following mechanism: ##STR3##
It should be noted that monomer b may itself be allyl glycidyl
ether which is commercially available from several sources.
Suitable cations include Na+, NH.sub.4 +, Ca+.sup.2 and K+.
After the desired monomers have been obtained, free radical chain
addition polymerization may proceed in accordance with conventional
solution polymerization techniques. Polymerization initiators such
as persulfate initiators, peroxide initiators, etc. may be used.
Preferably the requisite monomers are mixed with water and alcohol
(preferably isopropanol). The resulting polymer may be isolated by
well-known methods such as distillation, etc. or the polymer may
simply be used in its aqueous solution.
It should be mentioned that water soluble terpolymers comprising
monomers a and b of FORMULAE I or II may also be prepared for use
as deposit control agents and/or corrosion control agents. For
instance, AHPSE monomers may be incorporated into a water soluble
terpolymer backbone having other repeat units including acrylic
acid monomers, alkyl acrylate monomers, methacrylic acid monomers,
acrylamide monomers, etc.
The polymers are added to the aqueous system for which corrosion
inhibiting and/or deposit control activity is desired, in an amount
effective for the purpose. This amount will vary depending upon the
particular system for which treatment is desired and will be
influenced by factors such as, the area subject to corrosion, pH,
temperature, water quantity and the respective concentrations in
the water of the potential scale and deposit forming species. For
the most part, the polymers will be effective when used at levels
of about 0.1-500 parts per million parts of water, and preferably
from about 1.0 to 100 parts per million of water in the system to
be treated.
The water soluble polymers of the present invention are also used
with topping agents useful to enhance the inhibition of silica
deposition. Topping agents found to be particularly effective are
phosphonates. They may be added to the aqueous system in an amount
of from 1 to about 500 ppm. Preferably, the range is between 1 and
about 100 ppm.
Examples of preferred phosphonates are phosphonic acids. Those
utilized in the present invention include:
hydroxyethylidene diphosphonic acid (HEDP), Monsanto Dequest
2010
2-phosphonobutane-1,2,4 - tricarboxylic acid (PBSAM), Mobay
Bayhibit AM
hydroxypropylidene diphosphonic acid (HPDP), Betz Laboratories,
Inc.
hydroxybutylidene diphosphonic acid (HBDP), Betz Laboratories,
Inc.
hydroxyisobutylidene diphosphonic acid (HIBDP), Betz Laboratories,
Inc.
aminotri(methylenephosphonic acid) (AMP), Monsanto Dequest 2000
hydroxyphosphonocarboxylic acid (Belcor 575), Ciba Geigy
diethylene triamo-penta (methylene phosphonic acid), (Dequest 2060)
Monsanto
The water soluble polymer of the invention may be added to the
aqueous system either continuously or intermittently. It may be
blended with the chosen phosphonate prior to addition to the system
or, alternatively, both compounds may be added separately. The
phosphonates acid compound may also be added either continuously or
intermittently as conditions require, in order to maintain the
necessary concentrations.
EXAMPLES
Testing was conducted with Bench Top Recirculators which were
operated in batch configuration with no makeup or blowdown streams.
Treatment efficacy was determined from the appearance of the
stainless steel heat transfer surface, and turbidity of
recirculating water after 48 hours. Sump turbidity is measured in
standard NTU units which were derived from analysis with a
conventional turbidimeter.
Test Conditions
pH: 9.0
sump Temperature: 120 Deg. F.
Flow Rate: 3.0 GPM
Velocity Across Heat Transfer Surface: 2.1 Ft/Sec
Heat Flux through a Stainless Steel Tube: 15,600 BTU/ft*ft*Hr
Sump Volume: 12 Liters
Water Matrix
Ca.sup.+2 : 200 ppm as CaCO.sub.3
Mg.sup.+2 : 200 ppm as CaCO.sub.3
SiO.sub.2 : 200 ppm
NaHCO.sub.3 : 225 ppm
Table I exhibits test results using an acrylic
acid/allylhydroxypropyl-sulfonate ether copolymer, having a 3/1
monomer mole ratio and a high molecular weight, in combination with
various phosphonates.
TABLE I ______________________________________ POLYMER/PHOSPHONATE
BLENDS Deposition Sump Concentration Treatment Tube Turbidity (ppm)
Blend Deposit (NTUs) ______________________________________ (HEDP
Blends) polymer/HEDP 50/2.5 polymer/HEDP None 23 50/2.5
polymer/HEDP Hazy 36 50/2.5 polymer/HEDP V.L. 30 50/1 polymer/HEDP
Mod. 47 50/5 polymer/HEDP Light 26 50/10 polymer/HEDP Mod. 31 40/2
polymer/HEDP Mod. 32 25/2.5 polymer/HEDP Mod. 50 12.5/2.5
polymer/HEDP Heavy 22 100/10 polymer/HEDP Light 44 (PBSAM Blends)
50/2.5 polymer/PBSAM Mod. 53 50/10 polymer/PBSAM Mod. 19 100/5
polymer/PBSAM V.L. 36 100/10 polymer/PBSAM V.L. 38 100/10
polymer/PBSAM V.L. 34 100/10 polymer/PBSAM V.L. 36 50/20
polymer/PBSAM Mod. 30 (Other Phosphonate Blends) 50/2.5
polymer/HPDP Mod. 25 50/2.5 polymer/HBDP Mod. 22 50/2.5
polymer/HIBDP V.L. 33 50/2.5 polymer/HIBDP R Mod. 50/2.5
polymer/HDP(C-5) Light 50/2.5 polymer/AMP V.L. 43 50/2.5
polymer/Bel 575 Mod. 47 50/2.5 polymer/Deq.2060 Light
______________________________________ V.L. = Very Light Deposit
Mod. = Moderate Deposition polymer: acrylic
acid/alkylhydroxypropylsulfonate ether, 3/1 mole ratio
The acrylic acid:allylhydroxypropylsulfonate ether polymer/HEDP
blend was the only treatment to produce a clean deposition tube.
Optimum treatment levels under the given test conditions are 50 ppm
polymer and 2.5 ppm HEDP. Changing the treatment level or blend
ratio results in increased deposition on the heat transfer surface.
PBSAM was less effective then HEDP as evidenced by the moderate
deposition on the tube at the 50/2.5 ppm treatment blend ratio. AMP
was slightly less effective than HEDP along with HIBDP
(hydroxyisobutylidenediphosphonic acid).
The test results of Table I are arranged within Table II in
relation to their relative efficacies along with other comparative
treatments. Full names for abbreviated compounds not previously
defined will be provided following Table II.
TABLE II ______________________________________ RELATIVE EFFICACIES
OF VARIOUS TREATMENTS Treatment Concentration Ratio
______________________________________ MOST EFFICACIOUS
(Clean/Light deposit on tube, High Total SiO.sub.2) AA/AHPSE:HEDP
50:2.5 ppm AA/AHPSE:PBSAM 100:5 ppm AA/AHPSE:HIBDP 50:2.5 ppm
AA/AHPSE:AMP 50:2.5 ppm MODERATELY EFFICACIOUS (Moderate
Deposition, Total SiO.sub.2 > Reactive SiO.sub.2) AA/AHPSE:HEDP
50:5 ppm AA/AHPSE:HEDP 50:1 ppm AA/AHPSE:PBSAM 50:20 ppm
AA/AHPSE:HPDP 50:2.5 ppm AA/AHPSE:HEDP 50:10 ppm AA/AHPSE:PESA
50:50 ppm AA/AHPSE:PBSAM 50:1 ppm AA/AOP:PBSAM 100:10 ppm
AA/AHPSE:HEDP 100:10 ppm AA/AAPSE:PBSAM 50:10 ppm TAMOL
731:AlNH.sub.4 :HEDP 50:50:2.5 ppm AMPS/IPPA:AlNH.sub.4 :HEDP
50:50:25 ppm LEAST EFFICACIOUS (Heavy Deposition, Total SiO.sub.2 =
Reactive SiO.sub.2) polyacrylic acid.sup.1 50 ppm
PESA:AA/AHPSE.sup.2 :PBSAM 100:50:1 ppm SS/MA:HEDP 50:2.5 ppm
polyacrylic acid:PBSAM 10:1 ppm PESA:HEDP 50:2.5 ppm Dowfax
2Al:HEDP 50:2.5 ppm polyacrylic acid.sup. 1 :HEDP 50:6 ppm
PESA:PBSAM 100:5 ppm polymaleic acid:HEDP 50:2.5 ppm Ethaquad
18/25:Dequest 2060 50:12 ppm Tamol 731:PBSAM 50:3 ppm AA/APA:HEDP
50:2.5 ppm AA/AHPSE.sup.2 :PBSAM 50:1 ppm (NH.sub.4).sub.2 CO.sub.3
:PBSAM 50:10 ppm Borate:HEDP 100:2.5 ppm PBSAM 10 ppm
AA/AHPSE.sup.3 :PBSAM 100:10 ppm AA/AHPSE 50 ppm HEDP 2.5 ppm
AA/AMPS:PBSAM 100:10 ppm polyacrylic acid.sup.4 :HEDP 50:2.5 ppm
AA/AMPS:HEDP 50:2.5 ppm AA/AHPSE:HEDP 12.5:2.5 ppm AMPS/IPPA:HEDP
50:2.5 ppm PESA 100 ppm polymethacrylic acid:HEDP 50:2.5 ppm
PVP:HEDP 50:2.5 ppm PVA:HEDP 50:2.5 ppm
______________________________________ .sup.1 MW = @ 10,000 .sup.2
3:1 mole ratio, low molecular weight .sup.3 6:1 mole ratio .sup.4
MW = @ 2,200 PESA: poly(succinic acid ether) SS/MA: sulfonated
styrene/maleic acid Dowfax 2Al: oxybis (dodecylbenzenesulfonic
acid) Ethaquad 18/25: methylpolyoxyethylene(15)octadecylammonium
chloride Tamol 731: copolymer of maleic acid and diisobutylene
AA/APA: copolymer of acrylic acid and alkylphosphonic acid Borate:
boric acid/lignin/polysaccharide AMPS/IPPA: copolymer of
2acrylamide-2-methylpropylsulfonic acid and isopropanyl phosphonic
acid PVP: polyvinyl pyrrolidone PVA: polyvinyl alcohol
The foregoing data clearly demonstrate the value of the AA/AHPSE
copolymer, 3/1 mole ratio, along with various phosphonates to
control the deposition of silica in aqueous systems. The specific
concentrations of the chemical constituents may be varied in order
to optimize treatment efficacy. System parameters such as the pH
level, water temperature, flowrate and silica and other mineral
contents affect the function of the treatment chemicals. It may
therefore be necessary for the water system operator to vary the
concentration levels of the treatment chemicals within the
preferred ranges in order to effect the greatest possible silica
deposit inhibition.
While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and
modifications of this invention will be obvious to those skilled in
the art. The appended claims and this invention generally should be
construed to cover all such obvious forms and modifications which
are within the true spirit and scope of the present invention.
* * * * *